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Discussion

A and B are playing mathematical puzzles. A asks B "the whole numbers, greater than one, which can divide all the nine three digit numbers 111,222,333,444,555,666, 777,888 and 999?"

B immediately gave the desired answer. It was:

  • A.
    3, 37 and 119
  • B.3, 37 and 111
  • C.9, 37 and 111
  • D.3, 9 and 37

Answer: B

Every one of the nine numbers is a multiple of 111:

\[ 111,\ 222 = 2 \times 111,\ \ldots,\ 999 = 9 \times 111 \]

So any common divisor of all nine must divide 111, and conversely every divisor of 111 divides them all.

\[ 111 = 3 \times 37 \]

The divisors greater than 1 are therefore 3, 37 and 111. 9 is excluded because \( 111 \div 9 \) is not whole.

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